This disclosure relates to reinforced polyester compositions, method of manufacture, and articles thereof.
Thermoplastic polyester compositions, such as poly(alkylene terephthalates), have valuable characteristics including strength, toughness, high gloss, and solvent resistance. Polyesters therefore have utility as materials for a wide range of applications, from automotive parts to electric and electronic appliances. Because of their wide use, particularly in electronic applications, it is desirable to provide flame retardance to polyesters.
Numerous flame retardants (FR) for polyesters are known, but many contain halogens, usually chlorine and/or bromine Halogenated flame retardant agents are less desirable because of the increasing demand for ecologically friendly ingredients. Halogen-free flame retardants, such as phosphorus- and nitrogen-based compounds can be used as well. There is a need to improve the flame retardance of thin sections of molded compositions containing such flame retardants.
More ecologically compatible flame retardant (eco-FR) formulations based on aluminum salts of phosphinic or diphosphinic acid compounds and melamine compounds have been developed to overcome environmental issues of halogenated flame retardants. Another benefit of the eco-FR formulations is high comparative tracking index (CTI) compared to halogenated FR. CTI is a measure of the electrical breakdown on the surface of an insulating material. To measure the tracking, 50 drops of 0.1% ammonium chloride solution are dropped on the material, and the voltage measured for a 3 mm thickness. A large voltage difference gradually creates a conductive leakage path across the surface of the material by forming a carbonized track. Materials having a higher CTI require a higher voltage to generate a conductive leakage path.
However, the eco-FR formulations also possess undesirable mechanical properties, including reduced impact strength and tensile strength, as well as undesirable flow properties compared to the halogenated flame retardant compositions. The addition of small amounts of a polyetherimide (PEI), in particular ULTEM 1010, can boost mechanical properties of the eco-FR formulations, although with the drawback of lowering CTI (compared to eco-FR formulations without PEI. It is believed that PEI tends to form chars, reducing CTI.
Thus, an ongoing need exists for polyester compositions having the combination of high comparative tracking index and good flame retardant properties at thicknesses of 0.8 mm or less, while at least essentially maintaining, dimensional stability, mechanical properties and/or heat properties.